Originally published in England in 1973 as The Heartclock, by Dick Morland, this speculative novel is an early departure from the Dalziel and Pascoe crime novels for which Hill (The Wood Beyond) has become well known. In a country wracked by overpopulation, a teetering economy is sustained by severely regulating the population. Matt Matlock was the original sponsor of the bill that became the ""Age Law,"" requiring all English citizens to have a device installed in their hearts that will kill them when they reach 75, the current EOL, ""Expectation of Life."" Now that Matlock has reached the age of 69, however, he's having more than a few second thoughts about his draconian solution. Apparently, so are some others in high places, and they're all eager to get Matlock on their side as a persuasive figurehead. Although the thin futuristic veneer provided by hovercars and radio-telephones can't disguise this novel as serious SF, its strengths echo those of Hill's much better mysteries: a convoluted plot and twisty intrigue, and a main character as independent and intelligent as he is determined to succeed. (Jan.)